patch-from speed optimization (#3545)

* patch-from speed optimization: only load portion of dictionary into normal matchfinders

* test regression for x8 multiplier

* fix off-by-one error for bit shift bound

* restrict patchfrom speed optimization to strategy < ZSTD_btultra

* update results.csv

* update regression test

lib/compress/zstd_compress.c

@@ -4693,7 +4693,8 @@ static size_t ZSTD_loadDictionaryContent(ZSTD_matchState_t* ms,
             ip = iend - maxDictSize;
             src = ip;
             srcSize = maxDictSize;
-    }   }
+        }
+    }
 
     if (srcSize > ZSTD_CHUNKSIZE_MAX) {
         /* We must have cleared our windows when our source is this large. */
@@ -4702,22 +4703,31 @@ static size_t ZSTD_loadDictionaryContent(ZSTD_matchState_t* ms,
     }
 
     DEBUGLOG(4, "ZSTD_loadDictionaryContent(): useRowMatchFinder=%d", (int)params->useRowMatchFinder);
-    ZSTD_window_update(&ms->window, src, srcSize, /* forceNonContiguous */ 0);
-    ms->loadedDictEnd = params->forceWindow ? 0 : (U32)(iend - ms->window.base);
-    ms->forceNonContiguous = params->deterministicRefPrefix;
 
-    if (loadLdmDict) {
+    if (loadLdmDict) { /* Load the entire dict into LDM matchfinders. */
         ZSTD_window_update(&ls->window, src, srcSize, /* forceNonContiguous */ 0);
         ls->loadedDictEnd = params->forceWindow ? 0 : (U32)(iend - ls->window.base);
+        ZSTD_ldm_fillHashTable(ls, ip, iend, &params->ldmParams);
+    }
+
+    /* If the dict is larger than we can reasonably index in our tables, only load the suffix. */
+    if (params->cParams.strategy < ZSTD_btultra) {
+        U32 maxDictSize = 8U << MIN(MAX(params->cParams.hashLog, params->cParams.chainLog), 27);
+        if (srcSize > maxDictSize) {
+            ip = iend - maxDictSize;
+            src = ip;
+            srcSize = maxDictSize;
+        }
     }
 
+    ZSTD_window_update(&ms->window, src, srcSize, /* forceNonContiguous */ 0);
+    ms->loadedDictEnd = params->forceWindow ? 0 : (U32)(iend - ms->window.base);
+    ms->forceNonContiguous = params->deterministicRefPrefix;
+
     if (srcSize <= HASH_READ_SIZE) return 0;
 
     ZSTD_overflowCorrectIfNeeded(ms, ws, params, ip, iend);
 
-    if (loadLdmDict)
-        ZSTD_ldm_fillHashTable(ls, ip, iend, &params->ldmParams);
-
     switch(params->cParams.strategy)
     {
     case ZSTD_fast: